U.S. patent application number 14/906220 was filed with the patent office on 2016-06-09 for zoom lens, optical device, and method for manufacturing the zoom lens.
The applicant listed for this patent is NIKON CORPORATION. Invention is credited to Keiichi NAKAMURA.
Application Number | 20160161724 14/906220 |
Document ID | / |
Family ID | 52345921 |
Filed Date | 2016-06-09 |
United States Patent
Application |
20160161724 |
Kind Code |
A1 |
NAKAMURA; Keiichi |
June 9, 2016 |
ZOOM LENS, OPTICAL DEVICE, AND METHOD FOR MANUFACTURING THE ZOOM
LENS
Abstract
A zoom lens includes, in order from the object side: a first
lens group (G1) having positive refractive power, a second lens
group (G2) having negative refractive power, a third lens group
(G3) having positive refractive power, and a fourth lens group (G4)
having positive refractive power. Upon zooming from the wide angle
end state to the telephoto end state, the interval between each
lens group changes and the fourth lens group (G4) moves to the
image side after having once moved to the object side. The third
lens group (G3) has, in order from the object side, a positive
lens, a positive lens, and a negative lens. The zoom lens satisfies
the following conditional expression:
2.50<TLt/(fw*ft).sup.1/2<3.30, where TLt is the total length
of the zoom lens in the telephoto state, fw is the focal distance
of the total zoom lens system in the wide angle state, and ft is
the focal distance of the total zoom lens system in the telephoto
state.
Inventors: |
NAKAMURA; Keiichi; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NIKON CORPORATION |
Tokyo |
|
JP |
|
|
Family ID: |
52345921 |
Appl. No.: |
14/906220 |
Filed: |
June 26, 2014 |
PCT Filed: |
June 26, 2014 |
PCT NO: |
PCT/JP2014/003413 |
371 Date: |
January 19, 2016 |
Current U.S.
Class: |
359/687 |
Current CPC
Class: |
G02B 27/0025 20130101;
G02B 13/009 20130101; G02B 15/173 20130101; G02B 27/646 20130101;
G02B 15/16 20130101 |
International
Class: |
G02B 15/16 20060101
G02B015/16; G02B 27/00 20060101 G02B027/00; G02B 13/00 20060101
G02B013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 19, 2013 |
JP |
2013-150932 |
Claims
1. A zoom lens comprising, in order from an object: a first lens
group having positive refractive power; a second lens group having
negative refractive power; a third lens group having positive
refractive power; and a fourth lens group having positive
refractive power, wherein upon zooming from a wide-angle end state
to a telephoto end state, distances between respective lens groups
change and the fourth lens group moves to an image side after
having once moved to the object side, the third lens group
includes, in order from the object: a positive lens; a positive
lens; and a negative lens, and the following conditional expression
is satisfied: 2.50<TLt/(fw*ft).sup.1/2<3.30, where TLt
represents a total length of the zoom lens in the telephoto end
state, fw represents a focal length of a total system of the zoom
lens in the wide-angle end state, and ft represents a focal length
of a total system of the zoom lens in the telephoto end state.
2. The zoom lens according to claim 1, wherein the second lens
group comprises, in order from the object: a first negative lens: a
second negative lens: and a positive lens, and the following
conditional expression is satisfied:
0.50<-f2b/(fw*ft).sup.1/2<0.90, where f2b represents a focal
length of the second negative lens of the second lens group.
3. The zoom lens according to claim 1, wherein the following
conditional expression is satisfied: 0.40<f1/ft<0.80, where
f1 represents a focal length of the first lens group.
4. The zoom lens according to claim 1, wherein the following
conditional expression is satisfied: 4.8<f1/(-f2)<5.6, where
f1 represents a focal length of the first lens group, and f2
represents a focal length of the second lens group.
5. The zoom lens according to claim 1, wherein the following
conditional expression is satisfied: 1.94<Nd<2.50, where Nd
represents a refractive index with respect to d-line of the
negative lens of the third lens group.
6. The zoom lens according to claim 1, wherein the second lens
group includes a negative lens at least one surface of which is an
aspherical surface.
7. The zoom lens according to claim 1, wherein the fourth lens
group includes a positive lens and the following conditional
expression is satisfied: 0.5<(R42+R41)/(R42-R41)<2.0, where
R41 represents a paraxial radius of curvature of an object side
lens surface of the positive lens of the fourth lens group, and R42
represents a paraxial radius of curvature of an image side lens
surface of the positive lens of the fourth lens group.
8. The zoom lens according to claim 1, wherein the following
conditional expression is satisfied: 0.20<f3/f4<0.60, where
f3 represents a focal length of the third lens group, and f4
represents a focal length of the fourth lens group.
9. An optical device including the zoom lens according to claim
1.
10. A method for manufacturing a zoom lens including, in order from
an object: a first lens group having positive refractive power; a
second lens group having negative refractive power; a third lens
group having positive refractive power; and a fourth lens group
having positive refractive power, wherein upon zooming from a
wide-angle end state to a telephoto end state, distances between
respective lens groups are changed, the fourth lens group moves to
an image side after having once moved to the object side, the third
lens group includes, in order from the object: a positive lens; a
positive lens; and a negative lens, and each lens is disposed in a
lens barrel so that the following conditional expression is
satisfied: 2.50<TLt/(fw*ft).sup.1/2<3.30, where TLt
represents a total length of the zoom lens in the telephoto end
state, fw represents a focal length of a total system of the zoom
lens in the wide-angle end state, and ft represents a focal length
of a total system of the zoom lens in the telephoto end state.
Description
TECHNICAL FIELD
[0001] The present invention relates to a zoom lens, an optical
device, and a method for manufacturing the zoom lens.
TECHNICAL BACKGROUND
[0002] In recent years, for imaging optical systems such as video
cameras and digital still cameras, demands for high zoom ratio,
high performance over an total zoom range, and compactness have
become strong. As a zoom lens for meeting these demands, a zoom
lens comprising, arranged in order from an object along an optical
axis, a first lens group having positive refractive power, a second
lens group having negative refractive power, a third lens group
having positive refractive power, and a fourth lens group having
positive refractive power, that varies power by moving each lens
group, has been provided (for instance, refer to Patent Document
1).
PRIOR ARTS LIST
Patent Document
[0003] [Patent Document 1] Japanese Laid-Open Patent Publication
No. 2011-145674(A)
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0004] Zoom lenses that are more compact than conventional ones are
required.
[0005] The present invention is made by taking account of such a
problem, and aims at providing a compact zoom lens having excellent
optical performance, an optical device, and a method for
manufacturing the zoom lens.
Means to Solve the Problems
[0006] To achieve such objectives, a zoom lens according to the
present invention includes, in order from the object: the first
lens group having positive refractive power; the second lens group
having negative refractive power; the third lens group having
positive refractive power; and the fourth lens group having
positive refractive power. Upon zooming from a wide-angle end state
to a telephoto end state, distances between respective lens groups
are changed and the fourth lens group moves to the image side after
having once moved to the object side. The third lens group
includes, in order from the object: a positive lens; a positive
lens; and a negative lens, and satisfies the following conditional
expression:
2.50<TLt/(fw*ft).sup.1/2<3.30,
[0007] where
[0008] TLt represents a total length of the zoom lens in the
telephoto end state,
[0009] fw represents a focal length of a total system of the zoom
lens in the wide-angle end state, and
[0010] ft represents a focal length of a total system of the zoom
lens in the telephoto end state.
[0011] In the zoom lens according to the present invention, the
second lens group includes, in order from the object: a first
negative lens; a second negative lens; and a positive lens, and
preferably satisfies the following conditional expression:
0.50<-f2b/(fw*ft).sup.1/2<0.90,
[0012] where
[0013] f2b represents a focal length of the second negative lens of
the second lens group.
[0014] The zoom lens according to the present invention preferably
satisfies the following conditional expression:
0.40<f1/ft<b 0.80,
[0015] where
[0016] f1 represents a focal length of the first lens group.
[0017] The zoom lens according to the present invention preferably
satisfies the following conditional expression:
4.8<f1/(-f2)<5.6,
[0018] where
[0019] f1 represents a focal length of the first lens group,
and
[0020] f2 represents a focal length of the second lens group.
[0021] The zoom lens according to the present invention preferably
satisfies the following conditional expression:
1.94<Nd<2.50,
[0022] where
[0023] Nd represents a refractive index with respect to d-line of
the negative lens of the third lens group.
[0024] In the zoom lens according to the present invention, the
second lens group preferably includes a negative lens at least one
of the surfaces of which is an aspherical surface.
[0025] In the zoom lens according to the present invention, the
fourth lens group preferably includes a positive lens and
preferably satisfies the following conditional expression:
0.5<(R42+R41)/(R42-R41)<2.0,
[0026] where
[0027] R41 represents a paraxial radius of curvature of an object
side lens surface of the positive lens of the fourth lens group,
and
[0028] R42 represents a paraxial radius of curvature of the image
side lens surface of the positive lens of the fourth lens
group.
[0029] The zoom lens according to the present invention preferably
satisfies the following conditional expression:
0.20<f3/f4<0.60,
[0030] where
[0031] f3 represents a focal length of the third lens group,
and
[0032] f4 represents a focal length of the fourth lens group.
[0033] An optical device according to the present invention is
equipped with any one of the zoom lenses described above.
[0034] A method for manufacturing the zoom lens according to the
present invention is a production method of the zoom lens
including, in order from the object: the first lens group having
positive refractive power; the second lens group having negative
refractive power; the third lens group having positive refractive
power; and the fourth lens group having positive refractive power.
Upon zooming from the wide-angle end state to the telephoto end
state, the distances between respective lens groups are changed and
the fourth lens group moves to the image side after having once
moved to the object side. The third lens group includes, in order
from the object: a positive lens; a positive lens; and a negative
lens, and each lens is disposed in a lens barrel so that the
following conditional expression is satisfied:
2.50<TLt/(fw*ft).sup.1/2<3.30
[0035] where
[0036] TLt represents the total length of the zoom lens in the
telephoto end state,
[0037] fw represents the focal length of the total system of the
zoom lens in the wide-angle end state, and
[0038] ft represents the focal length of the total system of the
zoom lens in the telephoto end state.
Advantageous Effects of The Invention
[0039] According to the present invention, a compact zoom lens
having excellent optical performance, an optical device, and a
method for manufacturing the zoom lens may be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] FIG. 1 is a view illustrating a configuration of a zoom lens
according to Example 1 and a movement locus (arrow) of each group
from the wide-angle end state to the telephoto end state.
[0041] FIG. 2 is a view illustrating graphs showing various
aberrations of the zoom lens according to Example 1 upon focusing
on infinity, (a) in the wide-angle end state, (b) in an
intermediate focal length state, and (c) in the telephoto end
state.
[0042] FIG. 3 is a view illustrating a configuration of a zoom lens
according to Example 2 and a movement locus (arrow) of each group
from the wide-angle end state to the telephoto end state.
[0043] FIG. 4 is a view illustrating graphs showing various
aberrations of the zoom lens according to Example 2 upon focusing
on infinity, (a) in the wide-angle end state, (b) in the
intermediate focal length state, and (c) in the telephoto end
state.
[0044] FIG. 5 is a view illustrating a configuration of a zoom lens
according to Example 3 and a movement locus (arrow) of each group
from the wide-angle end state to the telephoto end state.
[0045] FIG. 6 is a view illustrating graphs showing various
aberrations of the zoom lens according to Example 3 upon focusing
on infinity, (a) in the telephoto end state, (b) in the
intermediate focal length state, and (c) in the wide-angle end
state.
[0046] [FIG. 7] (a) is a front view of a digital still camera, and
(b) is a rear view of a digital still camera.
[0047] FIG. 8 is a cross-sectional view along an arrow A-A' in FIG.
7(a).
[0048] FIG. 9 is a flowchart illustrating a method for
manufacturing the zoom lens.
DESCRIPTION OF THE EMBODIMENTS
[0049] Below, embodiments will be described with reference to the
drawings. The zoom lens ZL according to the present embodiment, as
illustrated in FIG. 1, includes: a first lens group G1 having
positive refractive power; a second lens group G2 having negative
refractive power; a third lens group G3 having positive refractive
power; and a fourth lens group G4 having positive refractive power.
The third lens group G3 includes, in order from the object: a
positive lens; a positive lens; and a negative lens. The third lens
group G3 is preferably constituted only of, in order from the
object, two positive lenses and one negative lens.
[0050] In the present embodiment, upon zooming from the wide-angle
end state to the telephoto end state, the first lens group G1 to
the fourth lens group G4 are moved so that the distances between
respective lens groups change. Also, in the present embodiment,
during zooming, a distance between the first lens group G1 and the
second lens group G2 is increased, a distance between the second
lens group G2 and the third lens group G3 is decreased, and a
distance between the third lens group G3 and the fourth lens group
G4 is increased. Furthermore, in the present embodiment, during
zooming, the fourth lens group G4 moves to the image side after
having once moved to the object side. Thus, due to the move of the
fourth lens group G4, the zoom lens ZL can be downsized.
[0051] Under the above configuration, the zoom lens ZL according to
the present embodiment satisfies the following conditional
expression (1):
2.50<TLt/(fw*ft).sup.1/2<3.30 (1),
[0052] where
[0053] TLt represents the total length of the zoom lens ZL in the
telephoto end state,
[0054] fw represents the focal length of the zoom lens ZL in the
wide-angle end state, and
[0055] ft represents the focal length of the zoom lens ZL in the
telephoto end state.
[0056] The conditional expression (1) specifies the total length of
the zoom lens ZL (a distance on the optical axis from the front
surface of the lens to the image surface) in the telephoto end
state. When the upper limit value of the conditional expression (1)
is exceeded, the total length of the zoom lens ZL becomes large
relative to the focal length and downsizing cannot be achieved. To
ease this, for instance, when power of the third lens group G3 is
made to be strong to aim at downsizing, spherical aberration and
chromatic aberration become worse. When the lower limit value of
the conditional expression (1) is not attained, since, for making a
focal length large with respect to the total length of the zoom
lens ZL, power of the first lens group G1 becomes strong, spherical
aberration and axial chromatic aberration become worse.
[0057] To ensure the effect of the present embodiment, the upper
limit value of the conditional expression (1) is preferably set at
3.29.
[0058] To ensure the effect of the present embodiment, the lower
limit value of the conditional expression (1) is preferably set at
2.80. To ensure the effect of the present embodiment further, the
lower limit value of the conditional expression (1) is preferably
set at 2.90.
[0059] In the zoom lens ZL according to the present embodiment, the
second lens group G2 includes, in order from the object, a first
negative lens, a second negative lens, and a positive lens, and
preferably satisfies the following conditional expression (2). The
second lens group G2 is preferably constituted, in order from the
object, only of two negative lens and one positive lens.
0.50<-f2b/(fw*ft).sup.1/2<0.90 (2),
[0060] where
[0061] f2b represents a focal length of the second negative lens of
the second lens group G2.
[0062] The conditional expression (2) specifies the focal length of
the second negative lens of the second lens group G2. When the
upper limit value of the conditional expression (2) is exceeded,
since power of the second negative lens of the second lens group
becomes weak, distortion in the wide angel end state becomes worse.
When the lower limit value of the conditional expression (2) is not
attained, astigmatism in the wide-angle end state becomes worse. By
a radius of curvature becoming small, since the distances to
neighboring lenses have to be secured, the zoom lens ZL becomes
large.
[0063] To ensure the effect of the present embodiment, the upper
limit value of the conditional expression (2) is preferably set at
0.80. To ensure the effect of the present embodiment further, the
upper limit value of the conditional expression (2) is preferably
set at 0.70.
[0064] To ensure the effect of the present embodiment, the lower
limit value of the conditional expression (2) is preferably set at
0.60. To ensure the effect of the present embodiment further, the
lower limit value of the conditional expression (2) is preferably
set at 0.65.
[0065] The zoom lens ZL according to the present embodiment
preferably satisfies the following conditional expression (3):
0.40<f1/ft<0.80 (3),
[0066] where
[0067] f1 represents the focal length of the first lens group
G1.
[0068] The conditional expression (3) specifies a relation between
the focal length of the first lens group G1 and the focal length of
the zoom lens ZL in the telephoto end state. When the upper limit
value of the conditional expression (3) is exceeded, the power of
first lens group G1 becomes weak, and distortion in the wide-angle
end state becomes worse. The lower limit value of the conditional
expression (3) is exceeded, the power of the first lens group G1
becomes strong, and spherical aberration and lateral chromatic
aberration in the telephoto end state become worse.
[0069] To ensure the effect of the present embodiment, the upper
limit value of the conditional expression (3) is preferably set at
0.70. To ensure the effect of the present embodiment further, the
upper limit value of the conditional expression (3) is preferably
set at 0.60.
[0070] To ensure the an effect of the present embodiment, the lower
limit value of the conditional expression (3) is preferably set at
0.50.
[0071] The zoom lens ZL according to the present embodiment
preferably satisfies the following conditional expression (4):
4.8<f1/(-f2)<5.6 (4),
[0072] where
[0073] f1 represents a focal length of the first lens group G1,
and
[0074] f2 represents a focal length of the second lens group
G2.
[0075] The conditional expression (4) specifies a relation between
the focal length of the first lens group G1 and the focal length of
the second lens group G2. When the upper limit value of the
conditional expression (4) is exceeded, the power of the first lens
group G1 becomes weak and distortion in the wide-angle end state
becomes worse. As the power of the second lens group G2 becomes
strong and the zoom ratio becomes large, the total length of the
zoom lens ZL becomes large. When the lower limit value of the
conditional expression (4) is not attained, the power of the second
lens group G2 becomes strong, and astigmatism and field curvature
become worse.
[0076] To ensure the effect of the present embodiment, the upper
limit value of the conditional expression (4) is preferably set at
5.4.
[0077] To ensure the effect of the present embodiment, the lower
limit value of the conditional expression (4) is preferably set at
5.0.
[0078] The zoom lens ZL according to the present embodiment
preferably satisfies the following conditional expression (5):
1.94<Nd<2.50 (5),
[0079] where
[0080] Nd represents a refractive index with respect to d-line of
the negative lens of the third lens group G3.
[0081] The conditional expression (5) specifies a proper refractive
index of the negative lens of the third lens group G3. When the
upper limit value of the conditional expression (5) is exceeded,
axial chromatic aberration in the telephoto end state becomes
worse. When the lower limit value of the conditional expression (5)
is not attained, since a Petzval sum is increased, field curvature
in the intermediate focal length state becomes worse.
[0082] To ensure the effect of the present embodiment, the upper
limit value of the conditional expression (5) is preferably set at
2.20.
[0083] To ensure the effect of the present embodiment, the lower
limit value of the conditional expression (5) is preferably set at
2.00.
[0084] In the zoom lens ZL according to the present embodiment, the
second lens group G preferably includes a negative lens at least
one surface of which is an aspherical surface. With such a
configuration, distortion, off-axis astigmatism, coma aberration,
and field curvature in the wide-angle end state can be excellently
corrected.
[0085] In the zoom lens ZL according to the present embodiment, the
fourth lens group G4 preferably includes a positive lens, and
satisfies the following conditional expression (6). The fourth lens
group G4, when being constituted of one lens satisfying the
conditional expression (6), the configuration may be simplified,
and a weight of the fourth lens group G4 that moves to the image
side after having once moved to the object side during zooming may
be lightened:
0.5<(R42+R41)/(R42-R41)<2.0 (6),
[0086] where
[0087] R41 represents a paraxial radius of curvature of an object
side lens surface of the positive lens of the fourth lens group G4,
and
[0088] R42 represents a paraxial radius of curvature of an image
side lens surface of the positive lens of the fourth lens group
G4.
[0089] The conditional expression (6) specifies a shape factor of
the positive lens of the fourth lens group G4. When the upper limit
value of the conditional expression (6) is exceeded, coma
aberration from the intermediate focal length state to the
telephoto end state becomes worse. When the lower limit value of
the conditional expression (6) is not attained, a variation of the
image surface from the intermediate focal length state to the
telephoto end state becomes large.
[0090] To ensure the effect of the present embodiment, the lower
limit value of the conditional expression (6) is preferably set at
1.0. To ensure the effect of the present embodiment further, the
lower limit value of the conditional expression (6) is preferably
set at 1.3.
[0091] The zoom lens ZL according to the present embodiment
preferably satisfies the following conditional expression (7):
0.20<f3/f4<0.60 (7),
[0092] where
[0093] f3 represents the focal length of the third lens group
G3,
[0094] f4 represents the focal length of the fourth lens group
G4.
[0095] The conditional expression (7) specifies a relation between
the focal length of the of the third lens group G3 and the focal
length of the fourth lens group G4. When the upper limit value of
the conditional expression (7) is exceeded, power of the fourth
lens group G4 becomes strong, spherical aberration and axial
chromatic aberration in a telephoto end state become worse, and a
total length of the zoom lens ZL becomes large due to an increase
in an amount of movement of the third lens group G3, thus
downsizing cannot be achieved. When the lower limit value of the
conditional expression (7) is not attained, power of the fourth
lens group G4 becomes weak and field curvature and coma aberration
in the wide-angle end state and coma aberration in a telephoto end
state become worse.
[0096] To ensure the effect of the present embodiment, the upper
limit value of the conditional expression (7) is preferably set at
0.50.
[0097] To ensure the effect of the present embodiment, the lower
limit value of the conditional expression (7) is preferably set at
0.30.
[0098] With to the zoom lens ZL according to the present embodiment
including the configuration described above, a compact zoom lens
having excellent optical performance may be achieved.
[0099] In FIG. 7 and FIG. 8, a configuration of a digital still
camera CAM (optical device), which is an optical device including
the above described zoom lens ZL, is illustrated. The digital still
camera CAM is so configured that, when a power button (not shown in
figures), is pressed, a shutter (not shown in figures) of a
photographic lens (zoom lens ZL) is opened, so that light from a
subject (an object) is converged by the zoom lens ZL and imaged
onto an imaging element C (for instance, CCD or CMOS) disposed at
an image surface I (refer to FIG. 1). A subject image that is
imaged on the imaging element C is displayed on a liquid crystal
monitor M disposed behind the digital still camera CAM. A
photographer, after determining a composition of a subject image
while viewing the liquid crystal monitor M, images the subject
image with the imaging element C by pressing down a release button
B1 and records and saves it in a memory (not shown in figures).
[0100] In the camera CAM, an auxiliary light emitting part EF for
emitting auxiliary light when a subject is dark and a function
button B2 used for a various conditional settings of the digital
still camera CAM and such are disposed. Although an example of a
compact type camera formed by integrating the camera CAM and the
zoom lens ZL is illustrated here, as an optical device, the present
invention may be applied to a single-lens reflex camera having a
body and a detachable lens barrel having the zoom lens ZL.
[0101] With the camera CAM according to the present embodiment
including the above described configuration, by mounting the above
described zoom lens ZL as a photographic lens, a compact camera
having excellent performance while having a high zoom ratio may be
achieved.
[0102] Next, with reference to FIG. 9, a method for manufacturing
the above described zoom lens ZL is described. In a barrel, each
lens is disposed (Step ST10) so that the first lens group G1 having
positive refractive power, the second lens group G2 having negative
refractive power, the third lens group G3 having positive
refractive power, and the fourth lens group G4 having positive
refractive power, are arranged in order from the object. Upon
zooming from the wide-angle end state to the telephoto end state,
distances between respective lens groups change and each lens is
disposed (Step ST20) so that the fourth lens group G4 moves to the
image side after having once moved to the object side. The third
lens group G3 is so configured that each lens is disposed (Step
ST30) so as to have the positive lens, the positive lens, and the
negative lens, in order from the object. Each lens is disposed
(Step ST40) so that the following conditional expression (1) is
satisfied:
2.50<TLt/(fw*ft).sup.1/2<3.30 (1),
[0103] where
[0104] TLt represents the total length of the zoom lens ZL in a
telephoto end state,
[0105] fw represents the focal length of the total system of the
zoom lens ZL in the wide-angle end state, and
[0106] ft represents the focal length of the total system of the
zoom lens ZL in the telephoto end state.
[0107] In one example of a lens arrangement according to the
present embodiment, for the zoom lens ZL as illustrated in FIG. 1,
in the first lens group G1 having positive refractive power, each
lens is incorporated in the barrel so that a negative meniscus lens
L11 with a convex surface facing the object side and a biconvex
shaped positive lens L12 are sequentially arranged in order from
the object. The negative meniscus lens L11 and the positive lens
L12 are cemented to constitute a cemented lens. As the second lens
group G2 having negative refractive power, each lens is
incorporated in the barrel so that a biconcave shaped negative lens
L21, a biconcave shaped negative lens L22, and a positive meniscus
lens L23 having a convex surface facing the object are sequentially
arranged in order from the object. As the third lens group G3
having positive refractive power, each lens is incorporated in the
barrel so that a biconvex shaped positive lens L31 and a positive
meniscus lens L32 having a convex surface facing the object, and a
negative meniscus lens L33 with a convex surface facing the object
side are arranged in order from the object. The positive lens L32
and the negative lens L33 are cemented to constitute a cemented
lens. As the fourth lens group G4 having positive refractive power,
a positive meniscus lens L41 having a convex surface facing the
object is incorporated in the barrel. Each lens is incorporated in
the barrel so that the conditional expression (1) described above
is satisfied (a corresponding value of the conditional expression
(1) is 3.1857).
[0108] According to the method for manufacturing the zoom lens ZL,
a compact zoom lens having excellent optical performance while
having a high zoom ratio may be produced.
EXAMPLES
[0109] Each Example according to the present embodiment is
described with reference to the drawings. Below, Table 1 to Table 3
are illustrated. These are tables of each specification in Example
1 to Example 3.
[0110] The use of reference numbers for FIG. 1 according to Example
1 is independent from the use of reference numerals in other
Examples to avoid complications of descriptions caused by increase
of digit numbers of reference numbers. Therefore, even if common
reference numbers are used to drawings associated with these
examples, those are not necessarily of a configuration common to
one another.
[0111] In each example, for calculation of aberration
characteristics, C-line (wavelength 656.2730 nm), d-line
(wavelength 587.5620 nm), F-line (wavelength 486.1330 nm) and
g-line (wavelength 435.8350 nm) are selected.
[0112] In the [Lens specifications] of the tables, a surface number
represents an order of an optical surface along a moving direction
of light ray from the object, R represents a radius of curvature of
each optical surface, D represents a distance to the next lens
surface which is a distance on the optical axis from each optical
surface to the next optical surface (or, the image surface), nd
represents a refractive index with respect to d-line of a material
of an optical member, and vd represents an Abbe number with respect
to d-line of a material of an optical member. The object plane
represents the object surface, (variable) represents a variable
distance to the next lens surface, curvature "co" represents a flat
surface or an aperture, (Stop S) represents an aperture stop S, and
the image plane represents the image surface I. The refractive
index of air "1.000000" is omitted. When an optical surface is an
aspherical surface, a symbol * is assigned to a surface number and
a paraxial radius of curvature is shown in a column for a radius of
curvature R.
[0113] In a table, for [Aspherical surface data], concerning an
aspherical surface shown in the [Lens specifications], a shape
thereof is represented by the next formula (a). X (y) represents a
distance along the optical axis direction from a tangential plane
at the apex of an aspherical surface to a position on the
aspherical surface at a height y, and R represents a radius of
curvature (paraxial radius of curvature) of a reference spherical
surface, .kappa. represents a conical coefficient, and Ai
represents an i-th aspherical surface coefficient. "E-n" represents
"x 10.sup.-n". For instance, 1.234E-05=1.234.times.10.sup.-5.
X(y)=(y.sup.2/R)/{1+(1-.kappa..times.y.sup.2/R.sup.2).sup.1/2}+A4.times.-
y.sup.4+A6.times.y.sup.6+A8.times.y.sup.8+A10.times.y.sup.10
(a)
[0114] In the [Entire specifications] of the tables, f represents a
focal length of the total lens system, FNo represents F number,
.omega. represents a half field angle (maximum incident angle,
unit:.degree.), Y represents an image height, Bf represents a
distance on the optical axis from the final surface of the lens (of
the fourth lens group G4) to the paraxial image surface, Bf
(air-equivalent) is a distance on the optical axis from the final
surface of the lens (of the fourth lens group G4) to the paraxial
image surface converted to an air equivalent distance, and TL
represents the lens total length (obtained by adding BF to the
length from the front surface of the lens to the final surface of
the lens on the optical axis).
[0115] In the [Zooming data] of the tables, valuable distance
values Di in each state of wide-angle end, intermediate focal
length, and telephoto end are shown. Where, Di represents a
variable distance between i-th surface and (i+1) surface.
[0116] In the [Zoom lens group data] of the tables, G represents a
group number, a group first surface represents a surface number of
a surface closest to the object of each group, a group focal length
represents a focal length of each group, and a lens configuration
length represents a distance on the optical axis from a lens
surface on the most object side to a lens surface on the most image
side of each group.
[0117] In the [Conditional expression] of the tables, values
corresponding to the above described conditional expressions (1) to
(7) are shown.
[0118] Although, below, for all specification values such as a
focal length f, a radius of curvature R, a distance to the next
lens surface D, and other lengths, "mm" is generally used unless
otherwise specified, since a zoom lens may have an equivalent
optical performance even when being proportionally enlarged or
proportionally reduced, specifications are not limited to these.
Also, unit is not limited to "mm", and other proper unit may be
used.
[0119] Descriptions of the tables are commonly applicable to all
the examples up to this paragraph, and descriptions of tables will
be omitted hereinafter.
Example 1
[0120] Example 1 will be described by using FIG. 1, FIG. 2, and
Table 1. A zoom lens ZL (ZL1) according to Example 1 is, as
illustrate in FIG. 1, constituted, in order from the object, of a
first lens group G1 having positive refractive power, a second lens
group G2 having negative refractive power, a third lens group G3
having positive refractive power, and a fourth lens group G4 having
positive refractive power.
[0121] The first lens group G1 is constituted, in order from the
object, of a cemented lens of a negative meniscus lens L11 with a
convex surface facing the object side and a biconvex shaped
positive lens L12. An image side lens surface of the positive lens
L12 is an aspherical surface.
[0122] The second lens group G2 is constituted, in order from the
object, of a biconcave shaped negative lens L21, a biconcave shaped
negative lens L22, and a positive meniscus lens L23 having a convex
surface facing the object. An image side lens surface of the
negative lens L21 is an aspherical surface.
[0123] The third lens group G3 is constituted, in order from the
object, of a biconvex shaped positive lens L31, and a cemented lens
of a positive meniscus lens L32 having a convex surface facing the
object and a negative meniscus lens L33 with a convex surface
facing the object side. Both surfaces of the positive lens L31 are
aspherical surfaces.
[0124] The fourth lens group G4 is constituted of a positive
meniscus lens L41 having a convex surface facing the object. An
image side lens surface of the positive meniscus lens L41 is an
aspherical surface.
[0125] In the present example, an aperture stop S aiming at
adjusting an amount of light is disposed on the object side from
the positive lens L31 located on the most object side of the third
lens group G3.
[0126] A filter group FL is disposed between the fourth lens group
G4 and the image surface I. The filter group FL is constituted of a
low pass filter for cutting spatial frequencies equal to or higher
than a limit resolution of a solid imaging element such an a CCD
disposed at the image surface I and an infrared cut filter.
[0127] The zoom lens ZL1 according to the present example is so
configured that, upon zooming from the wide-angle end state to the
telephoto end state, each lens group is moved so that a distance
between the first lens group G1 and the second lens group G2 is
increased, a distance between the second lens group G2 and the
third lens group G3 is decreased, and a distance between the third
lens group G3 and the fourth lens group G4 is increased. During the
zooming, the aperture stop S is integrally moved with the third
lens group G3.
[0128] The zoom lens ZL1 according to the present example performs
focusing from an infinite distance object to a finite distance
object by moving the fourth lens group G4 along the optical
axis.
[0129] In Table 1 below, each specification value in Example 1 is
shown. Surface numbers 1 to 21 in Table 1 correspond to optical
surfaces m1 to m21 shown in FIG. 1.
TABLE-US-00001 TABLE 1 [Lens specifications] Surface number R D nd
.nu.d Object plane .infin. 1 15.0662 0.5000 2.000690 25.46 2
11.5524 3.3000 1.618810 63.86 3* -740.1283 D3(variable) 4 -796.5513
0.4000 1.851350 40.10 5* 5.1061 2.2500 6 -93.1916 0.4000 1.883000
40.66 7 10.5842 0.3000 8 8.3583 1.2500 1.945950 17.98 9 30.7068
D9(variable) 10(Stop S) .infin. 0.2500 11* 4.8185 1.7000 1.593190
59.44 12* -13.4332 0.2000 13 3.9892 1.1000 1.677900 67.90 14
11.0682 0.3000 2.000690 29.14 15 3.0638 D15(variable) 16 8.9287
1.7000 1.531530 55.95 17* 28.7296 D17(variable) 18 .infin. 0.2100
1.516800 63.88 19 .infin. 0.3900 20 .infin. 0.5000 1.516800 63.88
21 .infin. 0.6000 Image plane .infin. [Aspherical surface data]
Surface number .kappa. A4 A6 A8 A10 3 1.0000 1.14795E-05
-9.86591E-09 0.00000E+00 0.00000E+00 5 0.9657 0.00000E+00
1.73093E-05 -2.56753E-07 7.39764E-09 11 0.0130 1.77585E-05
0.00000E+00 0.00000E+00 0.00000E+00 12 1.0000 4.07219E-04
0.00000E+00 0.00000E+00 0.00000E+00 17 1.0000 1.67439E-04
8.86060E-01 8.92770E-08 0.00000E+00 [Entire specifications] Zoom
ratio 11.29 Wide-angle Intermediate Telephoto end focal length end
f 4.64 23.70 52.39 FNo 3.51 5.55 6.45 .omega. 42.96 9.58 4.29 Y
3.50 4.05 4.05 Bf 5.50957 12.49373 4.00470 Bf(air-equivalent)
5.26766 11.95182 3.76279 TL 34.9700 42.6037 49.6713 [Zooming data]
Variable Wide-angle Intermediate Telephoto distance end focal
length end f 4.6402 23.6956 52.3902 D3 0.3916 10.6000 15.9000 D9
12.0396 2.0000 0.2959 D15 3.3792 4.1600 15.8208 D17 3.8096 10.4937
2.3047 [Zoom lens group data] Group Group first Group focal Lens
configuration number surface length length G1 1 28.83812 3.80 G2 4
-5.63224 4.60 G3 11 8.91180 3.30 G4 16 23.66763 1.70 [Conditional
expression] Conditional expression (1) TLt/(fw*ft).sup.1/2 = 3.1857
Conditional expression (2) -f2b/(fw*ft).sup.1/2 = 0.6891
Conditional expression (3) f1/ft = 0.5504 Conditional expression
(4) f1/(-f2) = 5.1202 Conditional expression (5) Nd = 2.001000
Conditional expression (6) (R42 + R41)/(R42 - R41) = 1.9019
Conditional expression (7) f3/f4 = 0.3765
[0130] From Table 1, it is understood that the zoom lens ZL1
according to the present example satisfies the conditional
expressions (1) to (7).
[0131] FIG. 2 is a view illustrating various aberration diagrams
(spherical aberration diagrams, astigmatism diagrams, distortion
diagrams, coma aberration diagrams, and lateral chromatic
aberration diagrams) of the zoom lens ZL1 according to Example 1,
and (a), (b), and (c) represent various aberration diagrams upon
focusing on infinity in the wide-angle end state, in the
intermediate focal length state, and in the telephoto end state,
respectively.
[0132] In each aberration diagram, FNO represents F number, A
represents an half field angel (unit: .degree.) for each image
height, and d, g, C, and F represent aberration in d-line, g-line,
C-line, and F-line, respectively. When no symbol is assigned, it
represents aberration with respect to d-line. In an astigmatism
diagram, a solid line represents a sagittal image surface and a
broken line represents a meridional image surface. For aberration
diagrams for each example described later, reference signs same as
those in the present example are used.
[0133] As it is clear from each aberration diagram illustrated in
FIG. 2, the zoom lens ZL1 according to Example 1 is excellently
corrected for various aberrations in each focal length state from
the wide-angle end state to the telephoto end state and has
excellent optical performance.
Example 2
[0134] Example 2 is described by using FIG. 3, FIG. 4, and Table 2.
A zoom lens ZL (ZL2) according to Example 2 is, as illustrated in
FIG. 3, constituted, in order from the object, of a first lens
group G1 having positive refractive power, a second lens group G2
having negative refractive power, a third lens group G3 having
positive refractive power, and a fourth lens group G4 having
positive refractive power.
[0135] The first lens group G1 is constituted, in order from the
object, of a cemented lens of a negative meniscus lens L11 with a
convex surface facing the object side and a biconvex shaped
positive lens L12. An image side lens surface of the positive lens
L12 is an aspherical surface.
[0136] The second lens group G2 is constituted, in order from the
object, of a biconcave shaped negative lens L21, a biconcave shaped
negative lens L22, and a positive meniscus lens L23 having a convex
surface facing the object. Both surfaces of the negative lens L22
are aspherical surfaces.
[0137] The third lens group G3 is constituted, in order from the
object, of a biconvex shaped positive lens L31, and a cemented lens
of a positive meniscus lens L32 having a convex surface facing the
object and a negative meniscus lens L33 with a convex surface
facing the object side. Both surfaces of the positive lens L31 are
aspherical surfaces.
[0138] The fourth lens group G4 is constituted of a positive
meniscus lens L41 having a convex surface facing the object. An
object side lens surface of the positive meniscus lens L41 is an
aspherical surface.
[0139] In the present example, an aperture stop S aiming at
adjusting an amount of light is disposed at a position further
toward the object side than the positive lens L31 located on the
most object side of the third lens group G3.
[0140] A filter group FL is disposed between the fourth lens group
G4 and the image surface I. The filter group FL is constituted of a
low pass filter for cutting spatial frequencies equal to or higher
than a limit resolution of a solid imaging element such as an a CCD
disposed at the image surface I and an infrared cut filter or the
like.
[0141] The zoom lens ZL2 according to the present example is so
configured that, upon zooming from the wide-angle end state to the
telephoto end state, each lens group is moved so that a distance
between the first lens group G1 and the second lens group G2 is
increased, a distance between the second lens group G2 and the
third lens group G3 is decreased, and a distance between the third
lens group G3 and the fourth lens group G4 is increased. During the
zooming, the aperture stop S is integrally moved with the third
lens group G3.
[0142] The zoom lens ZL2 according to the present example performs
focusing from an infinite distance object to a finite distance
object by moving the fourth lens group G4 along the axis.
[0143] In Table 2 below, each specification value in Example 2 is
shown. Surface numbers 1 to 21 in Table 2 correspond to optical
surfaces m1 to m21 shown in FIG. 3.
TABLE-US-00002 TABLE 2 [Lens specifications] Surface number R D nd
.nu.d Object plane .infin. 1 15.8948 0.5000 1.846660 23.80 2
12.3720 3.3000 1.592520 67.86 3* -243.0567 D3(variable) 4 -74.5845
0.4000 1.883000 40.66 5 6.1762 1.9000 6* -17.7965 0.6000 1.531100
55.91 7* 8.4247 0.3000 8 7.7131 1.1500 1.945950 17.98 9 17.3242
D9(variable) 10(Stop S) .infin. 0.2500 11* 5.3279 1.7000 1.589130
61.24 12* -11.5395 0.2000 13 3.8789 1.1000 1.568830 56.00 14
16.5298 0.3000 2.001000 29.14 15 3.3083 D15(variable) 16* 9.2913
1.7500 1.531100 55.91 17 67.0004 D17(variable) 18 .infin. 0.2100
1.516800 63.88 19 .infin. 0.3900 20 .infin. 0.5000 1.516800 63.88
21 .infin. 0.6000 Image plane .infin. [Aspherical surface data]
Surface number .kappa. A4 A6 A8 A10 3 1.0000 1.38077E-05
-1.27084E-08 0.00000E+00 0.00000E+00 6 1.0000 -1.42340E-03
1.07169E-04 -1.91048E-06 0.00000E+00 7 1.0000 -1.09820E-03
1.41958E-04 -2.83155E-06 0.00000E+00 11 -0.7203 5.27733E-04
0.00000E+00 0.00000E+00 0.00000E+00 12 1.0000 4.55539E-04
0.00000E+00 0.00000E+00 0.00000E+00 16 1.0000 -4.64422E-05
2.29199E-06 2.77043E-09 0.00000E+00 [Entire specifications] Zoom
ratio 11.29 Wide-angle Intermediate Telephoto end focal length end
f 4.64 23.70 52.39 FNo 3.48 5.11 6.25 .omega. 42.26 9.74 4.36 Y
3.15 4.05 4.05 Bf 4.95580 11.34227 5.42880 Bf(air-equivalent)
4.71390 11.10036 5.18690 TL 35.1430 43.0875 50.7915 [Zooming data]
Variable Wide-angle Intermediate Telephoto distance end focal
length end f 4.6350 23.7000 52.3863 D3 0.4000 11.1982 15.6478 D9
11.8494 2.0994 0.3004 D15 4.4878 4.9976 15.9645 D17 3.2558 9.6423
3.7288 [Zoom lens group data] Group Group first Group focal Lens
configuration number surface length length G1 1 28.36324 3.80 G2 4
-5.41785 4.35 G3 11 8.84779 3.30 G4 16 20.09955 1.75 [Conditional
expression] Conditional expression (1) TLt/(fw*ft).sup.1/2 = 3.2595
Conditional expression (2) -f2b/(fw*ft).sup.1/2 = 0.6855
Conditional expression (3) f1/ft = 0.5414 Conditional expression
(4) f1/(-f2) = 5.2351 Conditional expression (5) Nd = 2.001000
Conditional expression (6) (R42 + R41)/(R42 - R41) = 1.3220
Conditional expression (7) f3/f4 = 0.4402
[0144] From Table 2, it is understood that the zoom lens ZL2
according to the present example satisfies the conditional
expressions (1) to (7).
[0145] FIG. 4 is a view illustrating various aberration diagrams
(spherical aberration diagrams, astigmatism diagrams, distortion
diagrams, coma aberration diagrams, and lateral chromatic
aberration diagrams) of the zoom lens ZL2 according to Example 2,
(a), (b), and (c) represent various aberration diagrams upon
focusing on infinity in the wide-angle end state, in the
intermediate focal length state, and in the telephoto state,
respectively.
[0146] As it is clear from each aberration diagram illustrated in
FIG. 4, the zoom lens ZL2 according to Example 2 is excellently
corrected for various aberrations in each focal length state from
the wide-angle end state to the telephoto end state and has
excellent optical performance.
Example 3
[0147] Example 3 will be described by using FIG. 5, FIG. 6, and
Table 3. A zoom lens ZL (ZL3) according to Example 3 is, as
illustrate in FIG. 5, constituted, in order from the object, of a
first lens group G1 having positive refractive power, a second lens
group G2 having negative refractive power, a third lens group G3
having positive refractive power, and a fourth lens group G4 having
positive refractive power.
[0148] The first lens group G1 is constituted, in order from the
object, of a cemented lens of a negative meniscus lens L11 with a
convex surface facing the object side and a biconvex shaped
positive lens L12. An image side lens surface of the positive lens
L12 is an aspherical surface.
[0149] The second lens group G2 is constituted, in order from the
object, of a biconcave shaped negative lens L21, a biconcave shaped
negative lens L22, and a positive meniscus lens L23 having a convex
surface facing the object. Both surfaces of the negative lens L22
are aspherical surfaces.
[0150] The third lens group G3 is constituted, in order from the
object, of a biconvex shaped positive lens L31, and a cemented lens
of a positive meniscus lens L32 having a convex surface facing the
object and a negative meniscus lens L33 with a convex surface
facing the object side. Both surfaces of the positive lens L31 are
aspherical surfaces.
[0151] The fourth lens group G4 is constituted of a positive
meniscus lens L41 having a convex surface facing the object. An
object side lens surface of the positive meniscus lens L41 is an
aspherical surface.
[0152] In the present example, an aperture stop S aiming at
adjusting an amount of light is disposed at a position further
toward the object side than the positive lens L31 located on the
most object side of the third lens group G3.
[0153] A filter group FL is disposed between the fourth lens group
G4 and the image surface I. The filter group FL is constituted of a
low pass filter for cutting spatial frequencies equal to or higher
than a limit resolution of a solid imaging element such an a CCD
disposed at the image surface I and an infrared cut filter or the
like.
[0154] The zoom lens ZL3 according to the present example is so
configured that, upon zooming from the wide-angle end state to the
telephoto end state, each lens group is moved so that a distance
between the first lens group G1 and the second lens group G2 is
increased, a distance between the second lens group G2 and the
third lens group G3 is decreased, and a distance between the third
lens group G3 and the fourth lens group G4 is increased. During the
zooming, the aperture stop S is integrally moved with the third
lens group G3.
[0155] The zoom lens ZL3 according to the present example performs
focusing from an infinite distance object to a finite distance
object by moving the fourth lens group G4 along the optical
axis.
[0156] In Table 3 below, each specification value in Example 3 is
shown. Surface numbers 1 to 21 in Table 3 correspond to optical
surfaces m1 to m21 shown in FIG. 5.
TABLE-US-00003 TABLE 3 [Lens specifications] Surface number R D nd
.nu.d Object plane .infin. 1 17.7326 0.5000 1.846660 23.78 2
13.3470 3.4000 1.592010 67.05 3* -110.8383 D3(variable) 4 -105.5549
0.4000 1.883000 40.80 5 6.1013 2.0000 6* -20.8684 0.6000 1.531100
55.91 7* 8.0283 0.2000 8 7.2498 1.2000 1.945950 17.98 9 15.6043
D9(variable) 10(Stop S) .infin. -0.2500 11* 4.6510 1.7000 1.583320
59.28 12* -10.1220 0.1000 13 5.6957 1.2000 1.593190 67.90 14 9.5626
0.3000 2.000690 25.46 15 3.4990 D15(variable) 16* 9.1074 1.7000
1.531100 55.91 17 37.4766 D17(variable) 18 .infin. 0.2100 1.516800
63.88 19 .infin. 0.2800 20 .infin. 0.5000 1.516800 63.88 21 .infin.
0.6000 Image plane .infin. [Aspherical surface data] Surface number
.kappa. A4 A6 A8 A10 3 1.0000 1.29175E-05 -1.59138E-08 0.00000E+00
0.00000E+00 6 1.0000 -2.68748E-03 2.39176E-04 -6.12069E-06
0.00000E+00 7 -9.1589 0.00000E-03 1.94240E-04 -4.99263E-06
0.00000E+00 11 -0.8139 4.77568E-04 0.00000E+00 0.00000E+00
0.00000E+00 12 1.0000 5.18766E-04 0.00000E+00 0.00000E+00
0.00000E+00 16 1.0000 7.19064E-05 9.84249E-07 7.85238E-09
0.00000E+00 [Entire specifications] Zoom ratio 11.34 Wide-angle
Intermediate Telephoto end focal length end f 4.62 26.00 52.40 FNo
3.42 5.55 6.54 .omega. 42.25 8.94 4.31 Y 3.25 4.00 4.05 Bf 4.40403
8.19505 4.13603 Bf(air-equivalent) 4.16212 7.95314 3.89413 TL
35.1430 43.0875 50.7915 [Zooming data] Variable Wide-angle
Intermediate Telephoto distance end focal length end f 4.6161
23.0029 52.3960 D3 0.3966 12.2757 16.2054 D9 12.1178 2.8792 0.8025
D15 4.6870 10.2931 16.6618 D17 2.8880 6.6773 2.5943 [Zoom lens
group data] Group Group first Group focal Lens configuration number
surface length length G1 1 29.53701 3.90 G2 4 -5.52404 4.40 G3 11
8.47073 3.30 G4 16 22.19207 1.70 [Conditional expression]
Conditional expression (1) TLt/(fw*ft).sup.1/2 = 3.2700 Conditional
expression (2) -f2b/(fw*ft).sup.1/2 = 0.6969 Conditional expression
(3) f1/ft = 0.5637 Conditional expression (4) f1/(-f2) = 5.3470
Conditional expression (5) Nd = 2.000690 Conditional expression (6)
(R42 + R41)/(R42 - R41) = 1.6421 Conditional expression (7) f3/f4 =
0.3817
[0157] From Table 3, it is understood that the zoom lens ZL3
according to the present example satisfies the conditional
expressions (1) to (7).
[0158] FIG. 6 is a view illustrating various aberration diagrams
(spherical aberration diagrams, astigmatism diagrams, distortion
diagrams, coma aberration diagrams, and lateral chromatic
aberration diagrams) of the zoom lens ZL3 according to Example 3,
(a), (b), and (c) represent various aberration diagrams upon
focusing on infinity in the wide-angle end state, in the
intermediate focal length state, and in the telephoto state,
respectively.
[0159] As it is clear from each aberration diagram illustrated in
FIG. 6, the zoom lens ZL3 according to Example 3 is excellently
corrected for various aberrations in each focal length state from
the wide-angle end state to the telephoto end state and has
excellent optical performance.
[0160] According to the present embodiment, a compact zoom lens
having excellent optical performance while having a high zoom ratio
may be achieved.
[0161] For easier understanding of the present invention,
descriptions are made with structural features of the embodiments,
but needless to say, the present invention is not limited to
these.
[0162] Although, in the above described embodiments, four-group
configurations are shown, the present invention is applicable to
other group configurations such as five-group and six-group
configurations. Also, the present invention may include a
configuration in which a lens or a lens group is added on the most
object side or a configuration in which a lens or a lens group is
added on the most image side. Here, a lens group means a part
having at least one lens separated by an air interval to be changed
during zooming.
[0163] For instance, a lens group may be a single or a plurality of
lens groups or a focusing lens group for focusing from an infinite
distance object to a finite distance object by moving a partial
lens group along the optical axis. Such a focusing lens group may
be applied to autofocusing, and is also suitable for a motor drive
for autofocusing (by using an ultrasonic motor and such). Although,
in each example described above, the total fourth lens group G4 is
made to be a focusing lens group, a partial group of the fourth
lens group G4 may be made to be a focusing lens group.
[0164] A lens group may be a vibration proof lens group for
correcting image blurring generated by camera shake by moving a
lens group or a partial lens group so as to have a component in a
direction perpendicular to the optical axis or by rotating and
moving (swinging) in an in-plane direction containing the optical
axis. Although, in each embodiment described above, the total third
lens group G3 is made to be a vibration proof lens group, a partial
group of the third lens group G3 may be made to be a vibration
proof lens group.
[0165] A lens surface may be formed either of a spherical surface,
a flat surface, or an aspherical surface. Preferably a lens surface
is a spherical surface or a flat surface as it makes it easier to
implement lens processing, assemblies and adjustment, hence
degradation of optical performance caused by errors from
processing, assemblies, and adjustments is prevented. Moreover,
even when the image surface is deviated, degradation of optical
performance can be small. When a lens surface is an aspherical
surface, the aspherical surface may be any one of an aspherical
surface formed by grinding processing, a glass mold aspherical
surface formed by shaping glass into an aspherical surface shape
with a mold, or a complex type aspherical surface formed by forming
a resin into an aspherical surface shape on a surface of glass. A
lens surface may be a diffractive surface. A lens may be a
refractive index distribution type lens (GRIN lens) or a plastic
lens.
[0166] Although an aperture stop is preferably disposed near the
third lens group, a frame of a lens may substitute its role without
providing a member as an aperture stop.
[0167] Each lens surface may be applied with an antireflection film
having high transmittance for a wide wavelength range for reducing
flare and ghost, and achieving high optical performance with high
contrast.
EXPLANATION OF NUMERALS AND CHARACTERS
[0168] ZL (ZL1 to ZL3) Zoom lens [0169] G1 First lens group [0170]
G2 Second lens group [0171] G3 Third lens group [0172] G4 Fourth
lens group [0173] S Aperture stop [0174] FL Filter group [0175] I
Image surface [0176] CAM Digital still camera (optical device)
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